Methods of acquiring position information, particularly global measurement systems that use for example GPS (Global Positioning System) satellites, have been in widespread use. The positioning methods include for example a method of using wireless base stations on the ground in addition to the method using GPS satellites. Both of the positioning methods measure a distance from plural reference points placed at clearly identified positions to a positioning target and calculate a position of the positioning target by using a three-point method.
At that time, the distance from the positioning target to each of the reference points, which is regarded as base information, includes errors caused by positioning methods and positioning environment. Examples of the possible causes of these errors are the following. A first possible cause is a positioning sensor detecting a reflected wave of a reference radio wave, resulting in misidentification of a distance from the positioning target to the reference point as being longer than the actual distance. Secondly, when radio waves from the reference points are received by using a positioning sensor, the reception time and intensity of the radio waves may not be accurate due to a noise source including the same frequency.
Such influence ultimately appears as an error in the measurement result. As a result, the positioning sensor outputs a position that is different from the actual position. This error varies from several meters to several kilometers. In view of this, the following technologies are examples of the technologies to improve the measurement precision.
The following is the first technology. Firstly, a question signal is transmitted from a wireless station A that is placed at a clearly identified position, and a wireless station C that is placed at an unidentified position transmits a response signal. The response signal from wireless station C is received by wireless stations A and B placed at clearly identified positions, and an ellipse-shape is calculated from position data based on a transmission time of the question signal and a reception time of the response signal in a wireless station B placed at an identified position. In addition, a hyperbolic curve is obtained from the difference in the position data based on the reception time of the response signal from the wireless station C between the wireless station A and the wireless station B, both being placed at identified positions. Afterwards, two intersections of the hyperbolic curve and the ellipse are obtained. Based on the arrival direction of the radio wave, one of the intersections is determined to be a position of the wireless station C placed at an unidentified position.
The following is the second technology. One set of initial orientation data including plural orientation estimations is generated, and the workload is divided into a certain number of overlapping regions. Each of the orientation estimations is assigned to one or a plurality of any corresponding overlapping regions to form one or a plurality of clusters of the orientation estimations in one or plural overlapping regions, and a position of an object represented by each cluster of orientation estimations is estimated. By comparing the positions of the objects estimated in clusters in overlapping regions, whether or not any of the objects is an overlapping object is determined, and the overlapping objects are deleted. The positions of the remaining estimated objects are provided to generate a set of position estimations. The set of position estimations represents a set of orientation estimations, which is improved compared with the set of initial orientation estimations.
As another technology, there is a technology of correcting position and orientation information of a camera from a deflection between a captured image of a construction and prerecorded 3D data of the construction. With this technology, the positioning precision is improved without the need to place a number of reference points.
When positioning a current position of a mobile terminal with GPS, there is a positioning sensor in which an error range can be obtained. At that time, the error region of positioning of the mobile terminal is represented by an ellipse-shaped range involving a semi-major axis error, a semi-minor axis error, and an angle of the major axis.